Much effort has been directed to integrating hip implants into surrounding bone. Ideally, a hip implant would be placed into the femur, and thereafter bone would readily grow into the surface of the implant. To achieve this objective, many different surface technologies have been applied to hip implants. In some instances, the surface of the implant is roughened, grit-blasted, plasma-sprayed, or microtextured. In other instances, the surface is coated with a biological agent, such as hydroxylapatite (known as HA). In all of these instances, the goal is the same: Produce a surface on the hip implant into which surrounding bone will grow or bond.
Porous coatings have also been applied to surfaces of hip implants. Porous surfaces are often thin coatings applied to the metallic substrate of the implant. Bone surrounding the implant can only grow into the thin coating itself. Bone cannot grow through the coating and into the metallic substrate. The depth of bone growth into the implant is limited to the depth of the porous coating. Bone simply cannot grow completely through the implant or deeply into the body of the implant.